Artist's concept of Mars Polar Lander near the Martian south pole. Photo: NASA

NASA said Monday that it would begin a joint review with a military mapping agency to investigate images that may have pinpointed the location for the lost Mars Polar Lander spacecraft.

Officials with the National Imagery and Mapping Agency (NIMA) said last week that an analysis of images of the surface of Mars, taken by the Mars Global Surveyor (MGS) spacecraft orbiting the planet, turned up possible evidence for the spacecraft and associated components, including its aeroshell and parachute.

"NIMA researchers reviewed and assessed features seen in several images that they believe could be indicative of the lander and its protective aeroshell," NASA said in a statement Monday.

Both agencies provided few other details about the search, and did not release the images in question. In a separate statement, NIMA officials said they used "unclassified resources and techniques" to identify the lander in high-resolution MGS images taken between December 1999 and February 2000.

Finding the spacecraft in those images would be especially challenging, given its small size. The spacecraft is about two meters across, only slightly more than the 1.4-meter resolution of the sharpest MGS images. Thus, even in the best case the lander would appear as only a few off-color pixels, making a definitive discovery difficult.

NASA is skeptical of NIMA's claims, noting that the pixels thought to be the lander could be nothing more than noise. To resolve the issue, or at least come to a better understanding of the images, NASA and NIMA experts will continue their analysis of those images as well as others that MGS will take later in the year.

The spacecraft's discovery could answer the mysteries regarding its disappearance on December 3, 1999, the day the spacecraft was scheduled to land in the south polar regions of Mars. Communications with the spacecraft were halted as planned shortly before the spacecraft entered the Martian atmosphere, to resume shortly after landing. However, contact with MPL was never regained, and efforts to restore communications ended in February of 2000.

A review panel concluded last March that the most likely cause of MPL's failure to communicate were spurious signals generated by sensors on the spacecraft's landing legs when the legs deployed during the spacecraft's descent. Those signals led the spacecraft's computer to believe that the spacecraft had landed, so it turned off the descent engine even though the spacecraft was still 40 meters above the surface. The spacecraft hit the surface at 22 meters per second, an unsurvivable speed, the panel concluded.

Finding the spacecraft on the surface largely intact, however, could cause some reconsideration of those conclusions. It could also bolster claims that signals picked up by a radio telescope in late December 1999 early January 2000 were from the lander. The possibility that the weak signals, detected by 45-meter antenna at Stanford University, rejuvenated the search for the lander in late January and early February of last year. NASA enlisted several radio telescopes to listen for any signals from the lander, but none were detected.

NIMA officials said that they got involved with the search last year, when NASA supplied the agency with MGS images between January and May 2000 to conduct a joint search for the lander. A separate, independent search by NASA alone, taking place at the same time, failed to turn up any evidence for the lander.

NIMA was established by an act of Congress in 1996 to centralize several photointelligence groups within the Defense Department and Central Intelligence Agency. The agency describes its mission as one to provide "timely, relevant, and accurate imagery, imagery intelligence, and geospatial information in support of national security objectives." The agency is headquartered in the Maryland suburbs of Washington, DC, with offices elsewhere in the Washington area as well as St. Louis, Missouri.